The reproductive system of the terrestrial slug, Limax maximus, is regulated by neurohormones secreted by cells in the CNS. Three endocrine factors have been identified whose production and/or release appears to be photoperiodically controlled: a gonadal mitogenic factor (GMF) which is probably synonymous with the maturation hormone that induces general sexual development, a factor called glactogenin that stimulates albumen gland galactogen biosynthesis and an ovulation factor that induces egg-laying in mature animals. Standard cell biology techniques will be employed to isolate and purify these factors (gel exclusion and ion exchange chromatography and electrophoresis). GMF neurosecretory cells (NSC) will be identified by microautery of NSC groups prior to implantation of brains in immature slugs. Lesions will be sought that abolish 3H-thymidine incorporation into gonadal DNA. Isolation of galactogenin will permit the raising of antibody for eventual immunocytological identification of the cells of origin. Ovulation hormone cells in the right parietal ganglion will be studied electrophysically to determine if and how they differ in long and short-day brains. The projects in progress should result in one of the most complete descriptions of any pulmonate reproductive neuroendocrine system. Identification of both the substances being secreted and the cells that produce them should ultimately permit investigation of the basic physiological and cellular processes involved in photoperiodic control of the reproductive cycle in this potentially superior invertebrate model.